FROST-HARDENING STUDIES WITH LIVING CELLS: I. OSMOTIC AND BOUND WATER CHANGES IN RELATION TO FROST RESISTANCE AND THE SEASONAL CYCLE

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Abstract
The osmotic pressure and non-solvent space of the cells of various types of plant were estimated by the plasmolytic method and related to frost resistance and the seasonal cycle.Osmotic pressure always rises with hardening and falls with dehardening, and it generally reaches higher values or begins to rise earlier in the hardier species and varieties.The effect of osmotic pressure in reducing the amount of ice formation is enhanced in woody plants by the condition that only about half the cell volume is occupied by the osmotically active solution. The remainder, i.e., the non-solvent space, is shown to consist partly of bound water and must therefore represent hydrophilic colloid. This occupies an even larger proportion of the sap vacuole than of the protoplasm, and it increases notably with hardening. This change, besides reducing intercellular ice, is regarded as protecting the most vulnerable part of the cell, viz., the vacuole, from being frozen at very low temperatures.

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